Methods presently being carried out for coating substrates with metal, which are practical on a scale which would include, for example, continuous strip substrates in coil form, include electroplating and hot-dip coating. Metals commonly electroplated on such a scale include zinc, tin and chromium. Metals commonly hot-dip coated on such a scale include zinc, tin, aluminum, and lead.
Coating a substrate with a metal by electroplating requires a large capital expenditure for power supply, power control equipment, electrolytic cells, and the like. Operating expenses are high, as significant electrical power is required. Maintaining cell electrodes and electrolyte baths is difficult.
Coating a substrate by hot-dip coating requires less of a capital expenditure than electroplating, however, operating expenses are high for heating the substrate prior to its entrance into the molten bath, and maintaining the molten metal bath and strip handling equipment in the molten bath.
On a smaller scale than the above described prior art processes, vapor deposition in a vacuum is used for depositing many different metals on various substrates. However, maintaining a vacuum on a scale required for coating substrates, such as continuous strip in coil form, is not practical.
While coating a substrate with a metal by electroplating and hot-dip coating processes are widely used, and produce a good quality finished product, the capital expenditure and high operating expenses make an alternative process desirable.